A conventional X-ray diagnosis apparatus irradiates an X-ray from an X-ray tube to a patient, and detects the X-ray penetrated through the patient with an image intensifier (hereinafter referred to as I.I.), which changes the X-ray into a light and an imaging tube or a charge coupled device changes the light into an electronic signal or a flat panel detector (hereinafter called as a FPD) directly changes the X-ray into the electronic signal. Thus, an X-ray fluoroscopic image is obtained. The X-ray apparatus enables an operator to observe flow and movement of a contrast agent inside the patient on a display. Moreover, the fluoroscopic image is stored in a memory and used for various image processes, such as enlargement/contrast adjustment/space filter processes or minimum/maximum trace processes or subtraction process or adding process for removing a noise, and the like.
The subtraction process for obtaining a subtraction image of a part of the patient using the X-ray diagnosis apparatus is explained below. In order to perform the subtraction process, the fluoroscopic image, a mask image, and a contrast image are obtained. The fluoroscopic image is used for setting a position of an X-ray diaphragm and a compensation filter. The mask image and the contrast image are basic images to create the subtraction image. Hereinafter, an imaging for obtaining the fluoroscopic image is called a fluoroscopic imaging, and an imaging for obtaining a mask image and a contrast image is called a main imaging. In the fluoroscopic imaging, the operator sets X-ray fluoroscopic terms (X-ray tube voltage, X-ray tube current, fluoroscopic time, etc.), considering patient information, such as a patient age, sex, the portion of the body being imaged and other factors (such as, but not limited to, patient condition, pregnancy status, medical conditions, allergy to the contrast agent, specific needed nursing care). The X-ray is irradiated to the patient based on the fluoroscopic factors, and the fluoroscopic image is displayed on the display. The operator adjusts a position of a supporting unit for supporting the X-ray tube and the I.I., in order to position an imaging area at an appropriate part of the patient. The operator sets positions of the X-ray diaphragm and the compensation filter, observing the fluoroscopic image.
The main imaging starts after the X-ray diaphragm and the compensation filter are set. In the main imaging, the mask image and the contrast image are obtained in order. The mask image is aligned to the contrast image, and the subtraction process between these images is performed. The subtraction image is displayed on the display in a real time.
In the conventional X-ray diagnosis apparatus, the X-ray diaphragm and the compensation filter are fixed at such a position that the imaging area is adequate during the main imaging, such as during a bolus chase imaging where the X-ray and the I.I. automatically move. That is, wherever the X-ray tube and the I.I. move within the imaging area, the X-ray irradiated to the patient is not blocked or attenuated. However, since the X-ray diaphragm is fixed during the main imaging, the irradiation range of the X-ray is wide, the amount of the X-ray irradiated to the patient increases, and the influence of scattered X-ray appears. Moreover, since the compensation filter is fixed during the main imaging, X-ray halation partially remains. However, it is difficult to manually adjust the position of the X-ray diaphragm or the compensation filter according to a contour of the patient during the main imaging where the X-ray tube and the I.I. automatically move.